Even in the wealthy town of Weston, the mansion that Jim and Kim Pallotta are building is in a class by itself

WESTON - When their Georgian-styled manse is complete, Jim and Kim Pallotta will be able to while away an evening in a 12-seat theater. Or they could shoot billiards in the games room or spin vinyl records in the music room. Or they could wander the wine cellar with its separate wings to accommodate magnums and jeroboams.

And that's just the basement.

The Pallottas' estimated $21 million, 20-room fieldstone and slate edifice, stretching from Ash to Wellesley streets in this mansion-studded town, will have, upon completion, some 21,000 square-feet of living space - making it the fifth most spacious in the state, according to Warren Group records. (Original plans had called for 28,000 square feet of living space, but the prohibitive price spurred a scale-down.)

How big is 21,000 square feet? Consider: The Pallottas' house could fit 11 average-size Massachusetts homes or nearly half a football field.

Jim Pallotta, 49, who declined to speak on the record about his new home, is a co-owner of the Boston Celtics who earned $200 million in 2005 as US equities manager for Tudor Investment Corp., according to Institutional Investor's Alpha magazine. He and his wife, Kim, who is overseeing the design of the house, have two sons, one in college and one in high school. The Pallottas have made their home since 1990 in a Wellesley colonial that was assessed at $3.4 million last year. They have other homes on Nantucket and in Charleston, S.C.

Their new home is set on a 27.5-acre spread purchased from Regis College for $9.3 million, along with a smaller adjacent property acquired later. It is a thing of frustration for curiosity seekers. Stands of evergreens obstruct the view from the road and private drives leading to the house are blocked by black chain-link fence covered with opaque green mesh. Signs warn against trespassing and note: "Cameras in use."

The house has taken two years to build, along with a year of planning, making for an employment bonanza in the construction trades. In addition to an undisclosed number of subcontractors, the building team has included a heating, ventilation, and air-conditioning engineer, lighting designer, interior designer, architect, geotechnical engineer, civil engineer, landscape architect, structural engineer, and a general contractor, according to the plans on file at Town Hall.

In Weston, where real estate is among the priciest in the state and watchful eyes keep close tabs on property doings, there has been notably little opposition to the house. The Pallottas headed off criticism with a quick response to the concerns of town officials. The couple eliminated some outdoor lighting and planted trees that now shield the house from sight.

But when a palace rises in town, there is chatter.

"You'd need roller skates to go from one end to the other," quipped Judy Keller, who said the size of the house is legendary in Weston.

"It's out of character for Weston," said an 89-year-old Weston resident who declined to have her name printed because she is a widow and worried for her safety.

Others say that the house is not out of place on a parcel of its size.

"It's more like an estate," said Barrie Gollinger, a Weston resident and homemaker. "And that is different than a big, big house."

Mary Ann Davidson, a fellow Weston resident, noted that the Pallottas will pay the town large sums in property taxes.

"He's helping us out," Davidson said.

It isn't clear what the Pallottas' tax bill will be when the house is finished. Until construction is complete and the value can be fully assessed, the Pallottas are paying taxes only on the percentage of the house that is done. Already, though, the Pallottas sought a property tax abatement in fiscal year 2007, on the claim that their partially built house had been overvalued. They won. The town reduced their tax bill last year by $9,428.60, leaving a total of $125,772.53, according to town records.

"We filed a request that they review and to their credit, they corrected it," said Jeffrey Allen, the Pallottas lawyer.

Plans for the house call for the first floor to feature a four-car garage, a sunroom, a family room, a wood-paneled kitchen, a dining room with seating for 14, a breakfast room, and a living room. Jim Pallotta's office will be equipped with a bank of computers, much like his office in Boston at Rowes Wharf.

One half of the upper floor will be four bedrooms, two for the Pallottas' sons. The other half will be the Pallottas' suite, including a master bedroom with a coved ceiling, a master bathroom, a sitting room, an exercise room, and two walk-in closets, according to the plans.

Elsewhere on the property, an inground pool will stretch 50 feet by 20 feet, the plans state. A cabana will feature a kitchen, a bathroom, and a washer-dryer, and a carriage house with eight garage doors will house Jim Pallotta's muscle car collection.

A prospective neighbor of the Pallottas' on Ash Street, who declined to give his name, said the house is of little concern to him. It is obscured from the road, he said, and that's what matters.